Steady States of the Reactor–Distillation Column System for an A + B ⇄ C Reaction

The steady states of the reactor-distillation column recycle system are analyzed for the reaction A + B C at various feed compositions. The analysis is performed for an infinite column operated at total reflux. If the lightest component, A, is in excess, the complete conversion of the medium-boiling component, B, is impossible. If reactant B is in excess, there are three steady states, of which two are characterized by complete conversion of reactant A. In the case of a recycle system with a finite column, there is no continuum of steady states.     

Dynamic Process Operation Under Demand Response – A Review of Methods and Tools

Participating in electricity markets through demand response causes new requirements for optimizing process control of chemical plants. The last ten years have brought great advances in the formulation and solution of economic nonlinear model predictive control and state estimation to support operation of processes under dynamic constraints. However, gaps remain regarding the availabilities of suitable plant models capable of describing processes active in demand response as well as of robust schemes for state estimation and economic nonlinear model predictive control in commercial tools.     

Properties of Shock‐Compressed Carbogal. Equations of State for Carbogal and Plexiglas

This paper presents results from experimental studies of the properties of Carbogal (C₈F₁₆ or perfluoro1,3dimethylcyclohexane), at high pressures and temperatures, in particular, data on single compression and recompression, temperatures, and velocity of sound. Data are given on shockwave compressibility of porous Plexiglas with an initial density 10–60 times lower than the density of the solid sample. Thermodynamically complete equations of state for Carbogal and Plexiglas are developed on the basis of a model published previously and wellknown experimental data. It is shown that calculations using the developed equations of state are in agreement with available experimental data for Carbogal up to pressures of 70 GPa and for Plexiglas over the entire examined range of pressures.     

Physico‐Chemical Processes for Landfill Leachate Treatment: Experiments and Mathematical Models

Abstract

In this study, the adsorption of synthetic landfill leachate onto four kinds of activated carbon has been investigated. From the equilibrium and kinetics experiments, it was observed that coal based PAC presented the highest organic pollutants removal efficiency (54%), followed by coal based GAC (50%), wood based GAC (33%) and wood based PAC (14%). The adsorption equilibrium of PAC and GAC was successfully predicted by Henry‐Freundlich adsorption model whilst LDFA+Dual isotherm Kinetics model could describe well the batch adsorption kinetics. The flocculation and flocculation–adsorption experiments were also conducted. The results indicated that flocculation did not perform well on organics removal because of the dominance of low molecular weight organic compounds in synthetic landfill leachate. Consequently, flocculation as pretreatment to adsorption and a combination of flocculation–adsorption could not improve much the organic removal efficiency for the single adsorption process.     

State‐of‐the‐Art Adsorption and Membrane Separation Processes for Hydrogen Production in the Chemical and Petrochemical Industries

Abstract

This review on the use of adsorption and membrane technologies in H₂ production is directed toward the chemical and petrochemical industries. The growing requirements for H₂ in chemical manufacturing, petroleum refining, and the newly emerging clean energy concepts will place greater demands on sourcing, production capacity and supplies of H₂. Currently, about 41 MM tons/yr of H₂ is produced worldwide, with 80% of it being produced from natural gas by steam reforming, partial oxidation and autothermal reforming. H₂ is used commercially to produce CO, syngas, ammonia, methanol, and higher alcohols, urea and hydrochloric acid. It is also used in Fischer Tropsch reactions, as a reducing agent (metallurgy), and to upgrade petroleum products and oils (hydrogenation).

It has been estimated that the reforming of natural gas to produce H₂ consumes about 31,800 Btu/lb of H₂ produced at 331 psig based on 35.5 MM tons/yr production. It is further estimated that 450 trillion Btu/yr could be saved with a 20% improvement in just the H₂ separation and purification train after the H₂ reformer. Clearly, with the judicious and further use of adsorption or membrane technology, which are both classified as low energy separation processes, energy savings could be readily achieved in a reasonable time frame.

To assist in this endeavor of fostering the development of new adsorption and membrane technologies suitable for H₂, CO and syngas production, the current industrial practice is summarized in terms of the key reforming and shift reactions and reactor conditions, along with the four most widely used separation techniques, i.e., absorption, adsorption, membrane, and cryogenic, to expose the typical conditions and unit processes involved in the reforming of methane. Since all of the reactions are reversible, the H₂ or CO productivity in each one of them is limited by equilibrium, which certainly provides for process improvement. Hence, the goal of this review is to foster the development of adsorption and membrane technologies that will economically augment in the near term and completely revamp in the far term a typical H₂, CO or syngas production plant that produces these gases from natural gas and hydrocarbon feedstocks.

A review of the emerging literature concepts on evolving adsorption and membrane separations applicable to H₂ production is provided, with an emphasis placed on where the state‐of‐the‐art is and where it needs to go. Recommendations for future research and development needs in adsorbent and membrane materials are discussed, and detailed performance requirements are provided. An emphasis is also placed on flow sheet design modification with adsorption or membrane units being added to existing plants for near term impact, and on new designs with complete flow sheet modification for new adsorption or membrane reactor/separators replacing current reactor and separator units in an existing plant for a longer term sustainable impact.     

Membrane‐Based Hybrid Processes: A Review

Abstract

It has been widely recognized that membrane separation processes can offer many advantages over conventional mass transfer processes. A large number of membrane separation processes are currently being practiced in various sectors of industries. Despite the advantages, membrane processes often suffer from shortcomings when used individually. To overcome such limitations, membrane‐based hybrid processes have been developed to maximize the productivity of the target separation processes. In this review, the membrane hybrid processes reported in the literature are classified into several categories and chosen examples of the processes are presented to show the general trends in the development of membrane‐based hybrid processes.     

Selective Hydrogenation of Ethyne in Ethene‐Rich Streams on Palladium Catalysts,Part 2: Steady‐State Kinetics and Effects of Palladium Particle Size,Carbon Monoxide,and Promoters

Developments in the last three decades of kinetics of selective hydrogenation of ethyne in ethene‐rich streams on palladium catalysts are reviewed. Most of the studies can be described comprehensively by a model that assumes carbonaceous deposits (i) create irreversibly on the palladium surface small A types of active site (selective to ethene) and large E types of active site (selective to ethane), and (ii) are involved in hydrogenation of ethene on E _s sites on the support. The relative importance of these sites, with varying (i) reaction conditions, (ii) palladium dispersion, (iii) process modifiers, and (iv) promoters, is discussed.     

Electrochemical Single‐Cell Reactor for Treatment of Industrial Wastewater Composed of a Spent Textile Bath

Abstract

In the paper the electro‐oxidation of a spent dyeing bath, mediated by the Cl^?/Cl₂ redox couple, was studied and proposed for the treatment of textile wastewater as a technology alternative to hypochlorite oxidation. The work focused on the optimization of the electrochemical reactor. Particular attention was paid to the dependence of transport mechanisms and reaction rates on temperature, applied current, and hydrodynamic conditions in the reactor. The simultaneous production of H₂O₂ from the cathodic reduction of O₂, which could also react with the dye, was also assessed. The regime which controlled the reaction was determined from the Hatta number.     

Diphonix® Resin: A Review of Its Properties and Applications

Abstract

The recently developed Diphonix® resin is a new multifunctional chelating ion exchange resin containing geminally substituted diphosphonic acid ligands chemically bonded to a styrene-based polymeric matrix. Diphonix can be regarded as a dual mechanism polymer, with a sulfonic acid cation exchange group allowing for rapid access, mostly non-specific, of ions into the polymeric network, and the diphosphonic acid group responsible for specificity (recognition) for a number of metal cations. The Diphonix resin exhibits an extraordinarily strong affinity for actinides, especially in the tetra- and hexavalent oxidation states. Therefore the resin has potential for applications in TRU and mixed waste treatment and characterization, and in the development of new procedures for rapid actinide preconcentration and separation from environmental samples. Metal uptake studies have been extended to alkaline earth cations, to transition and post-transition metal species, and to metal sorption from neutral or near neutral solutions. Also the kinetic behavior of the resin has been investigated in detail. In view of the above applications the influence of the most commonly occurring matrix constituents (Na, Ca, Al, Fe, hydrofluoric, sulfuric, oxalic and phosphoric acids) on the uptake of actinide ions has been measured. This review paper summarizes the most important results obtained in the studies on the properties of the Diphonix resin and gives an overview of the applications already in existence or under development in the fields of mixed waste treatment, actinide separation procedures, treatment of radwaste from nuclear power and fuel processing plants, and removal of iron from copper electrowinning solutions.

     

A Review of: “Polycyclic Aromatic Hydrocarbons: Chemistry and Carcinogenicity”

Abstract

Ronald G. Harvey, Cambridge University Press, Cambridge 1991. 396 pages. £80. ISBN 0 521 36458 2.     

Optimization of Dynamic Interfacial Tension for Crude Oil–Brine System in the Presence of Nonionic Surfactants

In this study, interfacial tension (IFT) is measured between brine and crude oil (a sample of heavy oil from an Iranian oil reservoir) in the presence of two nonionic surfactants, KEPS 80 (Tween 80) and Behamid D, at different concentrations in order to optimize the concentrations of the surfactants. The surface response method is used to design the IFT measurement experiments. The experimental design and optimization is performed using the IFT as an objective function and temperature, concentration, and time as independent variables. In addition to the IFT measurement, various experiments such as stability tests of the surfactants in NaCl brine solutions, adsorption experiments on the carbonated rock surface, and phase behavior tests are performed to investigate the behavior of KEPS 80 and Behamid D in the enhanced oil recovery process. At the end, a model using the response surface statistical technique is designed for optimization of the concentrations of the surfactants, and a surfactant molecular migration mechanism is used for explanation of the dynamic IFT variation versus time. In the case of IFT experiments, the effect of surfactant concentration (at 1000, 3000, and 5000 ppm) on the dynamic IFT is investigated. The experiments are performed at four temperatures (25, 40, 50, and 67°C). The results show that the oil–brine IFT values can be reduced to about 4 mN m⁻¹ in the presence of Behamid D and to about 1 mN m⁻¹ in the presence of KEPS 80 at low concentrations.     

The Effects of Water and CO2 on the Reaction Kinetics in the Iron‐Based Low‐Temperature Fischer‐Tropsch Synthesis: A Literature Review

A review of kinetic models for the iron‐based Fischer‐Tropsch synthesis revealed some important areas of progress, namely (a) a transition from rate equations with a first order denominator (consistent with an Eley‐Rideal type mechanism) to Langmuir‐Hinshelwood expressions with a second order inhibition term; (b) whereas kinetic models originally specified full coverage of the catalytic surface, later models found the influence of vacant sites to be important; (c) whereas water or CO₂ was traditionally always included in the FT rate equations, the most recent lumped kinetic models do not account for any influence of water. It was further concluded that the perceived inhibiting influence of water on the FT rate may have been an indirect effect via the water‐gas‐shift reaction that changed the hydrogen and CO partial pressures.     

How to Attain Ultralow Interfacial Tension and Three-Phase Behavior with Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 1. Optimum Formulation for Simple Surfactant–Oil–Water Ternary Systems

Enhanced recovery of crude oil by surfactant flooding requires the attainment of an ultralow interfacial tension. Since Winsor’s work in the 1950s it has been known that a minimum interfacial tension and a concomitant three-phase behavior of a surfactant–oil–water system occurs when the interactions of the surfactant and the oil and water phases are exactly equal. It has been known since the 1970s that these conditions are attained when a linear correlation is satisfied between the formulation variables, which are characteristic parameters of the substances as well as the temperature. This first part of our review on how to attain ultralow interfacial tension for enhanced oil recovery shows how formulation scan techniques using these correlations are used to determine an optimum formulation and to characterize unknown surfactants and oils. The physicochemical significance of the original empirical correlation is reported as the surfactant affinity difference or hydrophilic–lipophilic deviation model. We report the range of accurate validity of, and how to test, this simple model with four variables.     

Kinetics and Selectivity of the Fischer–Tropsch Synthesis: A Literature Review

A critical review of the kinetics and selectivity of the Fischer–Tropsch synthesis (FTS) is given. The focus is on reaction mechanisms and kinetics of the water–gas shift and Fischer–Tropsch (FT) reactions. New developments in the product selectivity as well as the overall kinetics are reviewed. It is concluded that the development of rate equations for the FTS should be based on realistic mechanistic schemes. Qualitatively, there is agreement that the product distribution is affected by the occurrence of secondary reactions (hydrogenation, isomerization, reinsertion, and hydrogenolysis). At high CO and H₂O pressures, the most important secondary reaction is readsorption of olefins, resulting in initiation of chain growth processes. Secondary hydrogenation of α-olefins may occur and depends on the catalytic system and the process conditions. The rates of the secondary reactions increase exponentially with chain length. Much controversy exists about whether these chain-length dependencies stem from differences in physisorption, solubility, or diffusivity. Preferential physisorption of longer hydrocarbons and increase of the solubility with chain length influences the product distribution and results in a decreasing olefin-to-paraffin ratio with increasing chain length. Process development and reactor design should be based on reliable kinetic expressions and detailed selectivity models.